Different from the typical cellular communication, which allows a base station to send and receive signals to and from a terminal device, device-to-device communication (D2D communication) allows two or more terminal devices to directly send and receive signals to and from each other. D2D communication is thus expected to create a new utility form of terminals which is different from that of the typical cellular communication. Examples of possible application include information sharing through data communication between proximate terminal devices or in a group of proximate terminal devices, information distribution from installed terminal devices, and autonomous communication referred to as machine to machine (M2M) between machines.
D2D communication can also be used to offload data in order to address the considerably increased data traffic by a recent increase in smartphones. For example, there are sharply increased needs to send and receive the streaming data of moving images today. Moving images, however, generally have the large amount of data. Accordingly, moving images problematically consume a large number of resources in a radio access network (RAN). If terminals are appropriate for D2D communication (e.g. the terminals have a small distance between each other), it is thus possible to reduce the resources consumed in an RAN and the processing loads on the RAN by offloading moving image data onto D2D communication. In this way, D2D communication is beneficial for both communication service providers and users. Accordingly, D2D communication is today recognized as one of the important technical fields necessary for Long Term Evolution (LTE), and attracts attention in the 3rd Generation Partnership Project (3GP) standardization meetings.
For example, Non-Patent Literature 1 discloses a use case of D2D communication.